<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        const arr = [
            { 'id': '29', 'pid': '', 'name': '总裁办' },
            { 'id': '2c', 'pid': '', 'name': '财务部' },
            { 'id': '2d', 'pid': '2c', 'name': '财务核算部' },
            { 'id': '2f', 'pid': '2c', 'name': '薪资管理部' },
            { 'id': 'd2', 'pid': '', 'name': '技术部' },
            { 'id': 'd3', 'pid': 'd2', 'name': 'java研发部' }
        ]

        function toTree(arr) {
            const obj = {}
            const newArr = []
            arr.forEach(item => {
                item.children = []
                obj[item.id] = item
            })

            arr.forEach(item => {
                const parent = obj[item.pid]
                if (parent) {
                    parent.children.push(item)
                } else {
                    newArr.push(item)
                }
            });

            return newArr
        }

        function toTree2(arr, pid = "") {
            const newArr = []
            arr.forEach(item => {
                if (item.pid === pid) {
                    const children = toTree2(arr, item.id)
                    if (children.length) {
                        item.children = children
                    }
                    newArr.push(item)
                }
            })
            return newArr
        }

        console.log(toTree2(arr));
    </script>
</body>

</html>